The present invention relates to fire fighting installations. More particularly the invention relates to a drive source or a drive unit for feeding extinguishing medium into at least one spray head. In greater detail the invention relates to a drive source for feeding extinguishing medium into at least one spray head for extinguishing fire, the drive source comprising
a liquid source including liquid and a gas source including gas, PA1 mixing means for mixing the liquid of the liquid source and the gas of the gas source, PA1 and transportation means for leading the liquid and the gas into the spray head in such a manner that an extinguishing medium including a liquid component and a gas component is led to the spray head for releasing the extinguishing medium from the spray head in the form of a mixture of gas and liquid droplets. PA1 the gas source is alternatively connected to the second chamber of the first cylinder or to the second chamber of the second cylinder through a conduit system, whereto a directional valve is connected, PA1 the directional valve is by means of a control device arranged in a first operating position to keep a connection between the gas source and the second chamber of the first cylinder open and a connection between the second chamber of the second cylinder and an outlet conduit of the transportation means open and in a second operating position to keep a connection between the gas source and the second chamber of the second cylinder open and a connection between the second chamber of the first cylinder and the outlet conduit open.
It is known to use gas under pressure to drive out extinguishing liquid from a water container and to feed the extinguishing liquid further into spray heads or sprinklers, i.e. spray heads with release means. The release means is typically, but not necessarily, a glass ampoule reacting to heat by breaking and thus causing release.
It has not been possible to control the feeding of gas into liquid as accurately as desired with prior art means.
An extinguishing medium with very small droplets has been possible to obtain with certain types of spray heads or sprinklers. When the liquid is water, water mist is obtained. Water mist has proven to be effective and environmental friendly in fire extinguishing. Very small water droplets effectively absorb heat and have also an extinguishing effect. In addition the consumption of extinguishing liquid remains low. However, it has become a technical problem to provide such a device comprising pressure accumulators, said device being capable of emitting water mist including sufficiently small water droplets during a longer period. This occurs because the droplet size increases when the pressure accumulators are emptied, i.e. when pressure is reduced, at the end of the extinguishing process. The problem has partly been solved by mixing gas at the end of the extinguishing process, as presented in the International Patent Application with the publication number WO 94/08659. The gas can be the same gas that is used as propellant to initially drive out the extinguishing liquid and later to drive out the liquid component of the extinguishing medium containing gas. Owing to the gas mixture it has been possible to obtain extremely small water droplets.
Even if good results have been obtained by the last mentioned apparatuses, there has been a need to produce a drive source which is in a controlled manner able to mix gas in the extinguishing liquid, and in such a manner that the drop size remains relatively constant also for a long time and during discharge of a very large amount of extinguishing medium. There has also been a need to make the fire fighting installations as simple as possible including a wish to keep the number and volume of available gas and water containers as small as possible.